1. Field of the Invention
This invention relates to controlled absorption pharmaceutical compositions and, in particular, to a controlled absorption propranolol composition.
2. Description of the Prior Art
Propranolol (1-(isopropylamino)-3-(1-naphthyloxy)-2-propanol is a beta-adrenergic blocking agent and as such is a competitive inhibitor of the effects of catecholamines at beta-adrenergic receptor sites. The principal effect of propranolol is to reduce cardiac activity by diminishing or preventing betaadrenergic stimulation. By reducing the rate and force of contraction of the heart, and decreasing the rate of conduction of impulses through the conducting system, the response of the heart to stress and exercise is reduced. These properties are used in the treatment of angina of effort to reduce the oxygen consumption and increase the exercise tolerance of the heart. Propranolol is also used in the treatment of cardiac arrhythmias to block adrenergic stimulation of cardiac pacemaker potentials. Propranolol is also beneficial in the long term treatment of hypertension. Other uses of propranolol are in the treatment of migraine and anxiety.
Propranolol is normally administered as propranolol hydrochloride tablets. Propranolol hydrochloride tablets are marketed by Imperial Chemical Industries PLC (ICI) under the trade mark Inderal. The normal dosage regimen is 10-40 mg three or four times daily.
A major drawback of oral propranolol therapy is that propranolol is extensively and rapidly metabolised so that only a small proportion of the active ingredient reaches the systemic circulation after oral administration. Propranolol is absorbed from the gastro-intestinal tract with peak plasma concentrations occurring one to two hours after a single dose. It is excreted in the urine as free and conjugated propranolol and as metabolites.
A sustained release form of Inderal for once daily administration is available and is marketed by ICI under the trade mark Inderal LA. This form of propranolol while exhibiting a sustained release of the drug has a relatively poor bioavilability. Furthermore, the absorption varies considerably from individual to individual. Other sustained release forms of propranolol are described in U.S. Pat. Nos. 4,248,857 and 4,248,858.
It is an object of the present invention to provide a controlled absorption form of propranolol which is suitable for once daily administration and which is characterised by a high extent of absorption, which is largely invariable from individual to individual, and hence by a high bioavailability.